The pip-specific Path implementation has been removed, and all its
usages replaced by pathlib.Path. The tmpdir and tmpdir_factory fixtures
are also removed, and all usages are replaced by tmp_path and
tmp_path_factory, which use pathlib.Path.
The pip() function now also accepts pathlib.Path so we don't need to put
str() everywhere. Path arguments are coerced with os.fspath() into str.
adds VERBOSE custom log level between DEBUG and INFO
used when `-v` is given. Now require -vv to enable full debug output.
Messages can be logged with VERBOSE level to promote them to `-v` output instead of `-vv`
